This invention relates to improvements in medical instruments, and more particularly to urinary catheters.
One of the most common medical procedures is the insertion of a medical instrument into a body passage, for example the insertion of a catheter through the urethra into the bladder, and, despite great advances having been made in the prevention of infection in many areas, this procedure has continued to cause introduction of infection into the bladder.
It is standard practice for catheterisation to be performed only after the area around the urethra has been thoroughly cleaned, the catheter has been sterilised and the operator has donned surgical gloves and mask, and yet infection has still been common. The reason for this has now been deduced as resulting from bacteria which are present within the urethra itself particularly at its outer end, and which it is difficult if not impossible to remove prior to insertion of the catheter. As the catheter enters the urethra, therefore, it comes into contact with the bacteria and carries them along the urethra and into the bladder, thus causing infection. No amount of precleaning of the area external of the urethra will prevent this.
Several proposals have previously been made to prevent the catheter carrying bacteria along the body passage, but none of these have proved entirely successful. For example, U.S. Pat. Nos. 3,332,424 (Minteer), 3,908,635 (Vick) and 3,908,663 (Vick) describe catheters having a tube of thin flexible material and a rigid collar secured around one end of the catheter tube. In use, these catheters are operated by placing the collar around the entrance to the body passage and pushing the tube through the collar so that the tube progressively everts along the passage. In this way movement of the tube wall relative to the passage wall is reduced so that bacteria are less likely to be carried along the passage, but bacteria can nevertheless be forced into the leading open end of the tube as it everts. These bacteria are then redeposited further up the passage on continued eversion of the tube. While these previously proposed catheters are an improvement over a basic catheter tube they still cause a degree of contamination by carrying bacteria further up the passage.
U.S. Pat. No. 3,669,099 (Silverman) describes and claims a similar system to the above-described prior art in that it has everting tubing for contacting a body cavity wall, but in this case the ends of the tubing are secured and sealed to a rigid cylindrical tube surrounding the tubing, so that the tubing forms a closed toroidal chamber which is then filled with a fluid. A long cylindrical medical instrument PG,4 can then be pushed through the tubing, and the pressure of fluid causes the tubing to evert as the instrument passes through it. This previously-proposed arrangement is complex as a fluid inlet must be provided in the rigid tube for injection of fluid to an appropriate pressure, and the presence of the toroidal chamber makes the apparatus rather wide and therefore somewhat uncomfortable for the patient. It is also relatively expensive to manufacture.
U.S. Pat. No. 3,421,509 (Fiore) and West German Offenlegungsschrift No. 24 56 980 both have a urethral catheter in which the catheter tube is slidable within an impervious-walled sheath having a closure member in the form of overlapping flaps at its distal end. The sheath also has an external shoulder for engaging the mouth of the urethra to limit the extent of insertion of the sheath into the urethra. In Fiore the shoulder is stated to be about 1.5 inches from the distal end of the sheath.
U.S. Pat. No. 4,023,559 (Gaskell) also has a catheter tube slidable within an impervious-walled sheath which has a closure formation at its distal end through which the catheter tube can extend. No limiting shoulder is provided on the sheath to determine its extent of penetration.